The present invention relates to a transmission power control method and radio communications apparatus effective for control of transmission power in the cellular CDMA (Code Division Multiple Access) system.
In the CDMA system, a single frequency band is shared by a plurality of users. This results in the fact that a signal from another station acts as an interference wave and degrades the circuit quality of a local station. As a technology to solve this problem, transmission power control is used. Particularly, As a transmission power control method for following an interference signal that varies instantaneously, a transmission power control method via closed loop is known.
FIG. 12 shows an example of a conventional transmission power control method via closed loop. As shown in FIG. 12, in case a base station and a mobile station communicates with each other, the base station determines a transmission power bit from a radio wave received from the mobile station (S11), inserts the transmission power control bit in a transmission signal, and transmits the resulting signal to the mobile station. The mobile station receives the signal transmitted from the base station, extracts the transmission power bit (S15) and controls its variable power amplification means according to the instruction of the transmission power control bit (S16).
Similarly, the mobile station determines a transmission power bit from a radio waved received from the base station (S14), inserts the transmission power control bit in the transmission signal, and transmits the resulting signal to the base station. The base station receives the signal transmitted from the mobile station, extracts the transmission power bit (S12) and controls its variable power amplification means according to the instruction of the transmission power control bit (S13).
In case high-accuracy transmission power control is made via an aforementioned conventional transmission power control method, a high-accuracy variable power amplifier is required and high-accuracy control of a variable power amplifier is required. However, an attempt to perform variable power amplification control using a high-accuracy variable power amplifier results in an increased circuit scale and power consumption as well as reduced portability.